Despite numerous studies reporting on the unequal distribution of physicians across geographic areas in the U.S, there remains a dearth of research on whether health care is more accessible and quality is better in areas with more physician supply. Furthermore, the published studies do not provide convincing evidence on the nature of the relationship. Is it linear, whereby increasing supply is associated with steadily improved access and quality, or is there a threshold above which improvements in access and quality level off with increases in physician supply? The proposed project aims to fill these gaps in the literature by analyzing use large national datasets, which have not been used by prior research. The goal of the proposed project is to help build an evidence base that can inform physician workforce policy. It has the following specific aims: Specific Aim 1: To assess how physician supply affects access to care in terms of unmet needs and usual source of care. Specific Aim 2: To investigate the effect of physician supply on utilization of different types of health services, with a focus on (1) avoidable hospitalizations and ED visits for non-urgent problems, both types of utilization could be reduced through improved access to primary health care; and (2) supply-sensitive services, such as hospitalizations and visits to specialists. Specific Aim 3: To examine the effect of physician supply on (a) total annual health care expenditures and (b) annual expenditures on different types of health services, including doctor office visits, ED visits, and inpatient services. Specific Aim 4: To examine the effect of physicia supply on health care quality using measures from the AHRQ's program of Consumer Assessment of Healthcare Providers and Systems (CAHPS). The proposed project fits within the current AHRQ Research Portfolio areas of Value Portfolio and Innovations and Emerging Areas Portfolio. In particular, it will use the AHRQ's Medical Expenditure Panel Survey (MEPS) to assess how changes in physician supply affect health care access, use, expenditures, and quality for Americans, including the AHRQ's priority populations, such as children, women, elders, and those with chronic conditions.